1. Field of the Invention
The present invention relates to a method for forming a flange on an open end of a pipe, e.g., for vehicle exhaust pipes.
2. Description of the Related Art
FIGS. 11 and 12 show an example of a known vehicle exhaust pipe coupling structure. In FIG. 12, approximately rhombic-shaped coupling flanges 61, 62 (see FIG. 11) are welded to the outer peripheral ends of an upstream exhaust pipe 1 and a downstream exhaust pipe 2, respectively. A gasket 63 disposed between the coupling flanges 61, 62 and the exhaust pipes 1 and 2 are joined using bolts 64 and nuts 65.
Japanese Laid-Open Patent Publication No. H8-75063 discloses a connecting structure for an exhaust pipe, in which flanges are welded to the respective outer peripheries of a first exhaust pipe and a second exhaust pipe. The second exhaust pipe is fitted into the opening of one end of the first exhaust pipe. The flanges are joined by bolts and nuts.
However, since the coupling flanges 61 and 62 have to be affixed to the outer peripheries of the ends of the exhaust pipes 1 and 2 by welding in the above described known structure, stress concentrates at the weld, which can easily lead to cracks and breakage caused, e.g., by vehicle vibrations. In addition, the welding step requires additional labor and costs.